Self-centering drill bit with pilot tip, and process

ABSTRACT

Significantly improved resistance to breaking while drilling in metal can be realized in twist drill bits having a web thickness taper which is about twice the web thickness taper specified in Standards and in common use in the industry. This creates much shallower flutes and flies in the face of conventional wisdom in the art which holds that the web taper rate should be low to maximize the amount of flute volume available to convey chips and sawdust out of the hole. A flute length of about 1/2″ less than the flute lengths specified by the Standards makes it possible to have such a large taper rate but still control variations in tolerances for the flute length. It also provides a marking zone for placing size indicia on the drill bit shank outside the portion which is gripped by the chuck jaws of a power drill. The use of the new web taper rate, in conjunction with modifications to the tip geometry of a self-centering drill bit with pilot tip, produces a drill bit optimized both for metal and wood drilling which is strong enough to withstand the forces exerted on the bit while drilling in metal using a hand-held power drill, yet which need not be retracted from a 2×4 to clear sawdust prior to drilling a hole completely through the thickness of the wood.

CROSS-REFERENCE TO RELATED APPLICATION

This is a continuation of U.S. patent application Ser. No. 09/087,157,filed May 29, 1998, now U.S. Pat. No. 6,050,754 which claims priority toU.S. Provisional Patent Application Ser. No. 60/048,016 filed May 29,1997, and entitled “Improved Self-Centering Drill Bit with Pilot Tip”,the specification and drawings of which are herein expresslyincorporated by reference.

FIELD OF THE INVENTION

The invention relates to twist drill bits having flutes that extend froma tip of the drill bit to a termination point on the shank. The drillbit flutes define a web thickness which increases along the length ofthe flute from the tip to the termination point. The invention uses amuch steeper web taper rate than is used in the industry. It has beendiscovered that bits employing the present invention experiencesignificantly enhanced toughness and resistance to breakage in metal,yet still perform well in wood. This enhanced effect is particularlypronounced when the drill bit is driven by a portable drill.

BACKGROUND OF THE INVENTION

Conventional wisdom in the art holds that it is advisable to use arelatively shallow web taper rate in twist drills so that the flutedepth along the length of the flute is as great as practicable. Thisshould provide the maximum amount of volume to convey chips, swarf orsawdust back from the tip and out of the hole being drilled. Thisconvention is embodied in two Standards: The American Society ofMechanical Engineers (ASME B94.11M-1993), and The National AerospaceStandard of the Aerospace Industries Association of America, Inc., (NAS907) (hereinafter collectively referred to as “Standards”), both ofwhich Standards are specifically incorporated in their entireties byreference herein. The Assignee of the present invention has been sellingconventional Jobber-length, straight-shank drill bits which haveparameters that track the Standards, and which have conventional webthickness taper rates between 0.024 inches to 0.030 inches. Also, it hasbeen selling a self-centering drill bit with pilot tip under the BULLET®trademark having a web taper rate of about 0.027 inches per inch offlute length. This self-centering drill bit was designed with the enduser who uses a portable drill in mind, particularly one who desires abit which is optimized to drill in both metal and wood. The firstversions ofthese bits are disclosed in U.S. Pat. No. 4,968,193, issuedNov. 6, 1990, to Chaconas et al., and U.S. Pat. No. 5,288,183, issuedFeb. 22, 1994, to Chaconas et al., each of which is assigned to the sameAssignee of the present invention. The entire disclosures of each ofthese two patents are also specifically incorporated by referenceherein.

One of the needs of an operator who uses the bit in a hand-held powerdrill is increased toughness, or resistance to breaking (typically inthe flute portion of the drill bit). The increased robustness is neededbecause in metal drilling the portable power drill user putsconsiderable side stresses on the drill bit, not having the stabilitythat a drill press provides. However, the BULLET® drill bit, which wasoptimized to drill well both in metal and in wood, not only needsstrength while drilling metal, it also must drill holes through woodwith a minimum of “woodpeckering”, that is, repetitively retracting andreinserting the drill bit to clear the flutes of sawdust. There is alsoa need to enhance the BULLET® drill bit's longevity if it should besubjected to an overspeed condition in metal, as well as the strength inits tip portion. Finally, there is a need to reduce its tendency toproduce a disc in laminated materials.

SUMMARY OF THE INVENTION

It has been discovered that by defying convention, and instead, using aradically-increased web taper rate, a much more robust drill bit will becreated. In addition, it has been discovered that a particular range ofincreased web taper rates will not only provide sufficiently enhancedrobustness or strength when drilling in metal, it simultaneouslyprovides a bit which minimizes the amount of woodpeckering required whendrilling wood. Accordingly, it is an object of the present invention tomanufacture a twist drill bit having a web thickness taper rate over thelength of the flute which is about twice as great as the web taper rateof conventional drill bits, thereby providing significantly increasedresistance to breakage while drilling in metal, yet, for drill bitshaving nominal diameters of 0.250 inch or greater, enabling the user todrill holes in inch and one-half thick wood in one pass.

It is a particular object of the preferred embodiments of the inventionto provide a twist drill bit in which the web thickness increases fromthe tip to the shank portion at a uniform taper rate along the length ofthe flute in the range from about 0.050 inch to about 0.071 inch perinch of flute length. It is yet another particular object of thepreferred embodiments of the invention to provide a bit marking zone onthe shank portion of the drill bit which is outside of the area of theshank typically gripped by the jaws of a chuck in which the drill bit isinserted.

A feature by which the above objects may be attained is by forming theflutes with the web taper rate of the present invention along a flutelength which is less than the flute length specified for a predeterminedbit nominal diameter by the ASME B94. 11-M-1993 Standard, andspecifically by reducing the flute length by about 0.3 inch to about 0.7inch. Optimally, the flute length is reduced by about one-half inch, forall nominal diameters of the drill bits. A preferred feature is to formindicia such as the nominal size ofthe bit, in the marking zone, so thatin the engagement by the chuck of the bit shank does not erase theindicia.

Another feature by which the above objects can be attained is in themanufacturing process: causing relative axial movement between agrinding wheel and drill bit stock while rotating the drill bit stockabout its axis, grinding the flute having the desired flute length withthe web thickness taper rate of the present invention, then retractingthe grinding wheel from the drill bit stock upon reaching a point whichis a predetermined distance before the point at which the flute wouldterminate at the shank if the taper rate were to be maintained.

It is yet another object of the present invention to enhance therobustness of self-centering drill bits with pilot tip of the type soldunder the trademark BULLET®. One feature by which the above object canbe attained is by optionally providing the drill bit tip portion with afishtail angle of less than 180°. Yet another preferred feature is toform a chamfer adjacent the fishtail such that a cutting edge on thechamfer connects a cutting lip on the fishtail with the outer diameterof the drill bit. Still another preferred feature is to provide thepilot portion with a back taper in the axial direction. Anotherpreferred feature is to provide a back taper which is at least 1°negative. And yet another feature is to size the width or diameter ofthe pilot portion to be about one-half the nominal bit diameter.

Other objects, features and advantages of the present invention willbecome more fully apparent from the following detailed description ofthe preferred embodiments, the appended claims and the accompanyingdrawings.

BRIEF DESCRIPTION OF THE DRAWINGS

In the accompanying drawings, in which like reference characters in thesame or different Figures indicate like part:

FIG. 1 is a side elevational schematic view of a conventional drill bitto which a force F is applied to such an extent that the bit breaks,usually in the flute portion;

FIG. 2 is a side elevational schematic view of a twist drill bitaccording to the present invention in which a much higher force F mustbe applied to break the drill bit;

FIG. 3 is a side elevational schematic view of a twist drill bitaccording to another embodiment of the present invention to which aforce F is applied to cause the bit to break outside the flute portion;

FIG. 4 is a schematic detail view of the drill bits of FIGS. 2 and 3superimposed upon the drill bit of FIG. 1, employing the web taper ratesof the present invention;

FIG. 5 is similar to FIG. 4, but illustrating solely a web taper rate ofthe present invention, in combination with a pilot tip of the presentinvention;

FIG. 6 is similar to FIG. 5, but illustrating the web taper rate of thepresent invention in a conventional twist drill bit;

FIG. 7 is a view similar to the view of FIG. 5, illustrating anembodiment of the present invention in which the flute length is thesame as the conventional flute length;

FIG. 8 is an elevational schematic view of the process for forming theweb taper rate of the present invention;

FIG. 9 is an elevational detail schematic view of the tip portion of aself-centering drill bit having a pilot tip;

FIG. 10 is one embodiment of an improved tip portion according to thepresent invention;

FIG. 11 is another embodiment of the tip portion of the presentinvention;

FIG. 12 is yet another embodiment of the tip portion according to thepresent invention;

FIG. 13 is still another embodiment of the tip portion of the presentinvention;

FIG. 14 is partial enlarged elevational detail view of the bit of FIG. 9rotated to illustrate a secondary lip relief angle (“F2”); and

FIG. 15 is an enlarged schematic detail view of the process for forminga portion of the tip portion of FIG. 9.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

Referring first to FIG. 1, a conventional twist drill bit is showngenerally as 10, and includes a shank portion 12, a flute portion 14containing two flutes 16 and a tip portion 18. When drilling in metalwith a portable power drill, the drill bit 10 encounters greater thannormal forces F transverse to the axis of the drill bit, as shownschematically in FIG. 1. If the force F is great enough, the drill bitwill break or fail as shown at 15. Tests run on a quarter inch diameterconventional twist drill bit 10 found that the failure 15 occurredprimarily in the fluted portion 14, when the bit was subjected to a peakforce at failure in the range from 150 to 175 lbs.

A twist drill using the taper rate of the present invention is showngenerally as 20 in FIG. 2, and includes homogenous shank portion 22,flute portion 24 having two flutes 26, and a tip portion 28. In tests ofquarter inch nominal diameter twist drill bits incorporating the taperrate of the present invention, it took a peak force at failure in therange of 250 to 300 lbs. to break the bit. In most cases the breakoccurred not in the fluted portion 24, but in the strongest part of thebit, namely the shank portion 22. This result was attained using thesame hardness of the bit steel as conventional bits. The first threequarters of the fluted portion is maintained at full hard, decreasing toa lesser hardness from that point to the end of the shank.

FIG. 3 shows an alternate embodiment of a twist drill incorporating theweb thickness taper rate of the present invention, and illustrates itsability to perform well in wood while still exhibiting its enhancedstrength while drilling in metal. It has been found that a twist drillbit made according to the invention shown in FIG. 3 and having a nominalbit diameter of ¼″ can be used to drill a hole through a 1½″ thick pieceof wood 30, such as 2×4, without withdrawing the bit to clear thesawdust from the flutes and then reinserting the bit to finish the hole.Thus the present invention embodied in the twist drill bit shown in FIG.3 reduces the amount of “woodpeckering”, so that the operator can use a¼″ metal-drilling drill bit to drill a hole through the board 30 in onepass, as indicated by arrow 32. The web taper rates of the presentinvention are shown schematically in various drill bits in FIGS. 4through 7.

FIG. 4 schematically illustrates the web taper of the present invention(shown in short dashes) superimposed upon the web taper of aconventional bit (shown as long and short dashes). The profile of theconventional web taper is referred to as 34, and the web profile of thepresent invention is referred to as 36.

The most common drill bit used by the person operating a hand-held powerdrill is known as a “Jobber's-length, straight-shank drill bit”,specifications for which are common in the industry and are set out inthe Standards. These Standards collectively set forth commonly-acceptedranges of drill bit parameters for various nominal bit diameters', andfurther reflect conventional wisdom in the art of drill bit technology.As previously noted, these teachings hold that the more chips or sawdusta flute can remove from thd hole being drilled, the better. To that end,conventional wisdom in the art dictates that the web thickness shouldtaper outwardly from the tip towards the shank at a very gradual rate.For example, the NAS 907 Standard specifies that the web taper rate forTypes “A”, “B” and “J” straight shank, Jobber's length drill bits beuniform tapers of 0.017″, 0.024″ and 0.006″, respectively, withrespective tolerances of plus or minus 0.003″, plus or minus 0.003″, andplus or minus 0.002″, respectively. Indeed the taper rates ofconventional bits sold by the Assignee of the present invention followthis teaching. For example, certain drill bits sold under the DeWALT®trademark have a web taper rate of 0.024″ inches per inch of flutelength for drill bit nominal diameters up to and including {fraction(3/16)}″, and a web taper rate of 0.030 inches per inch of flute lengthfor drill bits having nominal diameters greater than {fraction (3/16)}inch. As previously noted, self-centering drill bits having pilot tipssold under the BULLET® trademark have a web taper rate of 0.027 inchesper inch of flute length.

Referring once again to FIG. 4, bits following the teaching of theStandards have flutes along the flute portion 24 which exit at atermination point 38 with the outer diameter of the shank portion 22,the shank portion being defined as the portion of the drill bit outsideof the portion that contains the flute and which is inserted in thechuck of a power drill. Here the web thickness of the conventional webprofile 34 increased from a thickness T to a thickness designated by 40at termination, leaving a relatively large flute depth 42 for receivingthe chips or sawdust. In marked contrast, the web taper profile 36 ofthe present invention exits the bit 20 at a flute termination point 44.This provides a much thicker web 46 at the flute termination point 44and yields a very small flute depth 48 at that point. Note that theflute grinding wheel has left a relatively large radius portion 50 atthe conventional flute termination point 38, but a relatively smallradius 52 at the flute termination point 44 of the present invention.

In one embodiment of the present invention a uniform web taper rate of0.068 inch per inch of flute length was found to provide durability thatfar exceeded expectations. The peak transverse force F at failureapplied to a rotating cantilever-mounted drill bit exceeded 250 lbs.(for a ¼ inch nominal diameter drill bit), with very acceptable chipremoval characteristics when drilling in metal. In another embodiment ofthe present invention with the same nominal diameter, the web thicknesstaper rate was set at 0.054 inches per inch of flute length (plus orminus 0.003 inches) for all sizes of drill bits from ⅛ inch nominaldiameter ½ inch nominal diameter. Not only did the drill bit exhibit thesame strength characteristics, but it reduced the amount ofwoodpeckering when drilling wood. It was able to drill a hole in 1½ inchthick wood (such as a 2×4) in one pass. The web thickness T at the tipor point in the preferred embodiment generally follows the NAS 907Standard, and for that matter, the other parameters of bits according tothe preferred embodiments generally follow one or more of the Chaconaset al. teachings or the Standards, unless otherwise specified herein.

The other drill bit parameters pertaining to the drill bit shown in FIG.4 and to the other embodiments are as follows: “D” stands for thenominal diameter of the drill bit; “BL” stands for the bit length (notethat it does not extend to the tip but instead to the axiallyforwardmost point of the bit where the flute cuts the outer diameter ofthe bit); “FL1” stands for the flute length of a flute having aconventional web thickness taper rate and is the flute length referredto in the previously-identified Standards; and “FL2” is the flute lengthof one of the preferred embodiments of the present invention, created bydiminishing FL1 by a predetermined amount MZ. As will be describedshortly, selecting FL2 in this fashion confers a double benefit upon thedrill bit of the present invention.

Still referring to FIG. 4, for the most part, the parameters justdescribed, and those in the Standards, pertain to a double-flute,straight shank, Jobber's length drill bit. However, it is believed thatthe concept of the present invention will also have utility in theenvironment of a drill bit with a single flute. In that case, instead ofmeasuring the taper rate of a web thickness T, the taper rate of theshortest radial distance between the flute and the axis 54 of the drillbit (T/2) would be specified. In either event, the preferred webthickness taper rate ranges from about 0.050 inch to about 0.071 inchper inch of flute length, and the flute length FL lies in the range fromabout 0.3 inch to about 0.7 inch less than the flute length specified bythe ASME Standard.

Ideally, MZ is about ½ inch for all nominal bit diameters in the rangeof from ⅛ inch through ½ inch. Although it is anticipated that the webtaper rate of the present invention will do well in a drill bit having aconventional chisel point or web-thinned point (such as a split point)as schematically shown in FIG. 6, it is particularly useful in theunitary metal/wood-drilling, self-centering drill bit with pilot tipdeveloped by the Assignee of the present invention, and as furtherdescribed in the Chaconas et al. patents cited above. These embodimentsof the drill bits incorporated the web-taper rate of the presentinvention are shown in FIGS. 4 and 5, which bits can be equipped withany of the tip portions 28 shown in FIGS. 9 through 13.

The nomenclature of the parameters for these embodiments are noted inFIGS. 9 and 11. The tip portion 28 includes a fishtail portion 56 and apilot portion 58 extending axially outwardly from the fishtail portion.The fishtail portion 56 includes fishtail cutting lips 62 arranged at afishtail angle 60. In this embodiment, the cutting lips extend from thepilot portion to the outer diameter of the drill bit. The pilot portion58 extends a distance “L” from the fishtail portion 56, and has adiameter “d” smaller than the nominal diameter “D” of the drill bit. Thepilot portion 58 defines an annular pilot wall 64 which is both radiallyand axially relieved as taught in the above-identified Chaconas et al.patents. The pilot portion 58 is formed with pilot cutting lips arrangedat a point angle 68 (for example 135°) and, in the preferred embodiment,defines a split point 66. The pilot portion 58 is joined to the fishtailportion 56 with a radially-relieved fillet 70 having a radius “R”. Thedrill bit has the following parameters: the fishtail angle 60 is greaterthan 180°, namely about 190°, and the pilot wall 64 defines an axialback taper 65 of about 5°. For the purposes of this description, theback taper on the pilot 58 which is directed radially inwardly from thepoint end 66 of the bit 20 toward the fishtail portion 56 will beconsidered a “positive” angle, whereas a back taper which is directedradially outwardly, as identified as 67 in FIG. 13, will be considered a“negative” back taper angle. A negligible back taper angle is shown as69 in the embodiment shown in FIG. 12. For the purposes of thisdescription, “negligible” means in the range from greater than minus 1°to less than positive 1°. Other parameters noted in FIG. 9 are also usedin the embodiments shown in FIGS. 10 through 13 and include the pilotlength “L”, pilot diameter “d” and point angle 68.

Referring now to the embodiment shown in FIG. 10, it was discovered thatthe fishtail portion 56 will exhibit increased longevity if the fishtailangle 60 is reduced to lie in the range from about 168° to about 182°,and preferably about 170°. It has also been discovered that the pilotportion 58 will exhibit increased longevity if its diameter d isapproximately one-half the nominal bit diameter D.

Yet another discovery was made that adding a chamfer portion 72, asshown in FIG. 11, significantly improves the life of the bit 20 if itwere to be run at an overspeed condition. The chamfer portion 72includes at least one chamfer 74, and in the preferred embodimentincludes two chamfers. The chamfers 74 are oriented at a chamfer angle76 which is in the range of from about 75° to about 140°, and ispreferably about 90°. In the single-chamfer embodiment, the chamferangle 78 is about 45°, or one-half the two-chamfer included angle 76.The length of the chamfer 80 is in the range of from about 5% to about15% of the nominal diameter and is preferably about 10%. Anotheradvantage of the chamfer is the significant reduction in creation of“discs” in composite materials. Furthermore, in the embodiment shown inFIG. 11, the included angle 68 remains at 135°, but the preferred backtaper angle is in the range from 0° to 5.5°, with the preferred anglebeing 5°. Other tip parameters for the embodiment shown in FIG. 11 areset forth in TABLE 1.

TABLE 1 TABLE OF TIP PARAMETERS Nom. Bit Diam. Pilot Diam. Pilot LengthSecondary Lip Fillet Radius (In.) (In.) (In.) Relief Angle (In.) D d Lf2 R 1/8 .067 .05  14° .020  9/64 .072 .052 14° .020  5/32 .080 .052 14°.020 11/64 .087 .052 14° .020  3/16 .094 .052. 14° .020 13/64 .102 .05214° .023  7/32 .109 .056 14° .023 15/64 .117 .061 14° .023 1/4 .125 .06414° .023 17/64 .133 .068 14° .026  9/32 .141 .073 14° .026 19/64 .148.077 14° .026 5/16 .156 .08  14° .026 21/64 .164 .085 14° .030 11/32.172 .089 14° .030 23/64 .180 .093 14° .030 3/8 .188 .097 14° .030 25/64.195 .101 12° .035 13/32 .203 .105 12° .035 27/64 .211 .109 12° .035 7/16 .219 .113 12° .035 29/64 .227 .117 12° .035 15/32 .234 .121 12°.035 31/64 .242 .125 12° .035 1/2 .250 .129 12° .035

The embodiment shown in FIG. 12 is very similar to that of FIG. 11,except the back taper angle 69 is negligible. Similarly, the embodimentshown in FIG. 13 uses a negative back taper angle greater than minus 1°.

Referring now to FIG. 15, the process for generating the pilot portion58, the fishtail portion 56 and the radially-relieved fillet 70 isshown. The area of the pilot diameter relief is shown at 82; the filletrelief area is shown at 84, and the area of fishtail cutting lips reliefis shown as 86. It will be appreciated that in the drill bit of FIG. 15,a continuous cutting edge is created by the fishtail cutting lip 62,fillet edge 71 and pilot wall cutting edge 65. In order to enable theseedges to cut satisfactory, they all must be provided with reliefsurfaces as shown in FIG. 15, and as discussed in Chaconas et al, citedabove. To form such surfaces, a grinding wheel 88 having a grindingwheel face 90 is oriented with the bit axis 54, such that the fishtailangle 60 divided by two is in the desired range. The pilot back taperangle 65 (positive or negative) is achieved by providing the grindingwheel 88 with a predetermined form, which also defines the shape of thefillet 70. To generate the desired edges and surfaces, the bit ispositioned in the desired angular relationship to the grinding wheel 88and is rotated about its axis 54 in the direction shown by arrow 92 andat the same time is moved into the wheel in the direction shown by arrow94, thereby achieving the reliefs for the cutting edge 65, 71 and 62.The process is repeated on the opposite side of the bit to generate bothsets of cutting edges and reliefs.

Returning now to the web thickness taper rate of the present invention,it was discovered that a modification to the Standard flute lengthsresulted in benefits both in reducing variations in flute lengthtolerances as well as in creating a special marking zone “MZ” where suchindicia 96 as bit size may be formed, to thereby stay clear of the jawsof the drill chuck to which the bit is inserted (see FIG. 4). This meansthat the drill chuck will not eradicate the size markings from theshank, as often happens in conventional drill bits.

Again referring to FIG. 8, a grinding wheel 98 is positioned at apredetermined angle relative to the axis 54 of drill bit 20 and isbrought radially inwardly into contact with the bit at the tip portion28, or starting point of the flute, as shown by arrow 100. The bit stock20 and the grinding wheel 98 are then caused to have relative movementtowards one another along 30 an axial direction 102. In the preferredembodiment, the grinding wheel 98 is held for movement only in theradially inward and outward directions as shown by arrows 100, and thebit stock 20 is moved axially into the grinding wheel. A cam then causesthe grinding wheel 98 to move radially outwardly while the bit stockmoves into it, thereby creating a desired web taper rate. If thegrinding wheel 98 producing the taper rate of the present invention wereto be retracted at the termination point 38, creating a flute length FLIcorresponding to the flute length recommended by the Standards, thevariation in manufacturing tolerances of the grinding wheel and bit, incombination with the taper angle, would create a flute length FLI ofunacceptable breadth of variability as shown at 106. Inasmuch as theflute length is a very important parameter in the manufacture of twistdrill bits, it is preferable to maintain such variations to be within aplus or minus ⅛″, namely ¼″, in breadth. To reduce the variation influte length tolerances, it was discovered that if the grinding wheel 98were retracted radially outwardly at termination point 44, rather thanat 38, the variation in flute lengths could be significantly reduced.The point of retraction is determined by the flute length FLI diminishedby amount MZ, where MZ is in the range of from 0.3 inch to about 0.7inch, and preferably about ½ inch.

The process is completed when a second flute is formed diametricallyopposite the flute just described using the same process. In thepreferred embodiments, the process forms a modified parabolic flute.

Although the web thickness taper rate of drill bits of the presentinvention is believed to significantly improve the strength of drillbits having conventional point geometry, as schematically shown in FIG.6, it was particularly effective in enhancing the durability of drillbits having tip configurations 28 shown in FIGS. 9 through 13. Thecoaction of the web taper rate, pilot width, back taper angle, andchamfer of the embodiment shown in FIG. 11, will produce a twist drillbit of significantly improved strength overall while keeping theversatility that has help make it a commercial success.

The above-described embodiments, of course, are not to be construed aslimiting the breath of the present invention. Modifications, and otheralternative constructions, will be apparent which are within the spiritand scope of the invention as defined in the appended claims.

What is claimed is:
 1. A twist drill bit, comprising: a homogenous shankportion, a fluted portion and a tip portion adjacent the fluted portion;the fluted portion defining two flutes extending from the tip portionand terminating at the homogenous shank portion, the flutes having apredetermined flute length; the flute portion further defining a web;the web adjacent the tip portion having a predetermined web thickness;and the web thickness increasing from the tip portion to the homogenousshank portion such that during peak force failure the bit breaks in theshank portion.
 2. The drill bit claimed in claim 1, wherein the bit hasa predetermined nominal diameter, and wherein the flute length lies inthe range of from about 0.3 inch to about 0.7 inch less than the flutelength specified for said predetermined diameter by the ASMEB94.11-M-1993 Standard or its current revision, whichever Standard islater.
 3. The drill bit claimed in claim 2, and wherein the flute lengthis approximately one-half inch less than the flute length specified forsaid predetermined diameter by the ASME B94.11-M-1993 Standard or itscurrent revision, whichever Standard is later.
 4. The drill bit claimedin claim 1, further comprising a bit marking zone on the shank portionadjacent the termination of said flutes, the axial length of the bitmarking zone being in the range of from about 0.3 inch to about 0.7inch, and wherein the bit is marked in said bit marking zone withpredetermined indicia.
 5. The drill bit claimed in claim 1, furthercomprising a bit marking zone on the shank portion adjacent thetermination of said flutes, the axial length of the bit marking zonebeing approximately one-half inch, and wherein the bit is marked in saidbit marking zone with size indicia.
 6. The drill bit claimed in claim 1,wherein: the tip portion includes a fishtail portion and a pilot portionextending axially outwardly from the fishtail portion in a directionaway from the shank portion; the fishtail portion having a predetermineddiameter and cutting lips arranged in a predetermined fishtail angle;and the pilot portion having a predetermined diameter smaller than thefishtail portion diameter.
 7. The drill bit claimed in claim 6, whereinthe pilot portion defines an outer surface having a back taper extendingtoward the fishtail portion in an axial direction at a predeterminedback taper angle.
 8. The drill bit claimed in claim 6, wherein saidfishtail angle is less than 180°.
 9. The drill bit claimed in claim 8,wherein said fishtail angle lies in the range of from about 168° toabout 178°.
 10. The drill bit claimed in claim 9, wherein said fishtailangle is about 170°.
 11. The drill bit claimed in claim 7, wherein saidback taper angle is positive.
 12. The drill bit claimed in claim 11,wherein said back taper angle lies in the range offrom about 1° to about5.5°.
 13. The drill bit claimed in claim 12, wherein said back taperangle is about 5°.
 14. The drill bit claimed in claim 7, wherein saidback taper angle is at least 1° negative.
 15. The drill bit claimed inclaim 7, wherein said back taper angle is negligible.
 16. The drill bitclaimed in claim 6, wherein said pilot portion defines pilot cuttinglips formed in a web-thinned point.
 17. The drill bit claimed in claim16, wherein said pilot portion defines a split point.
 18. The drill bitclaimed in claim 6, wherein said fishtail portion further includes achamfered portion.
 19. The drill bit claimed in claim 18, wherein thechamfered portion is adjacent said cutting lips and has a chamferextending at a predetermined chamfer angle with respect to the axis ofsaid drill bit radially outwardly from at least one of said cutting lipsand in an axial direction towards said shank portion.
 20. The drill bitclaimed in claim 19, wherein a chamfer connects each cutting lip to theouter diameter of the drill bit.
 21. The drill bit claimed in claim 20,wherein there are two chamfers, and the two chamfers define a chamferincluded angle in the range of from about 75° to about 140°.
 22. Thedrill bit claimed in claim 21, wherein the chamfer included angle isabout 90°.
 23. The drill bit claimed in claim 19, wherein the chamferangle is about 45°.
 24. The drill bit claimed in claim 6, wherein thediameter of the pilot portion lies in the range of about 38 percent toabout 52 percent of the nominal drill bit diameter.
 25. The drill bitclaimed in claim 24, wherein the diameter of the pilot portion isapproximately one-half of the nominal drill bit diameter.
 26. The drillbit claimed in claim 1, wherein the drill bit is a Jobber-length,straight-shank drill bit.
 27. The drill bit claimed in claim 1, whereinsize indicia are formed on the shank portion outside the area to beengaged by the chuck jaws of a power drill.
 28. The drill bit claimed inclaim 1, wherein the flutes are parabolic.
 29. The drill bit claimed inclaim 6, wherein the fishtail angle is approximately 180°.
 30. The drillbit claimed in claim 6, wherein the fishtail angle is greater than 180°.31. The drill bit claimed in claim 2, wherein the flute terminates atthe shank in a radiused portion.
 32. The drill bit claimed in claim 1,wherein the web thickness increases from the tip portion to the shankportion at a uniform rate in the range of about 0.050 inch to about0.071 inch per inch of flute length.
 33. The drill bit claimed in claim1, wherein the flute length is selected so that when drilling a piece ofwood 1½ inch thick, the operator does not have to clear the flutes ofsaw dust and can drill through the entire thickness of the wood in onepass.
 34. A process for making a straight-shank twist drill bit having atip, a homogenous shank and two flutes defining a predetermined webthickness at the tip, comprising: orienting a grinding wheel having apredetermined diameter at a predetermined angle relative to the axis ofa piece of drill bit stock for generally transverse movement towards andaway from said drill bit stock; aligning said grinding wheel with thetip of said drill bit stock to remove a sufficient amount of material tocreate a predetermined web thickness at said tip when said two fluteshave been formed; and causing relative axial movement between saidgrinding wheel and said drill bit stock while rotating said drill bitstock about its axis to grind a flute having a predetermined flutelength in said bit, such that said flute has a web-thickness thatincreases from the tip to the homogenous shank such that during peakforce failure the bit breaks in the shank.
 35. The process claimed inclaim 34, further comprising retracting said grinding wheel from contactwith said drill bit stock upon reaching a point which is a predetermineddistance prior to the point at which the flute would terminate at theshank if said taper rate were maintained.
 36. The process claimed inclaim 35, wherein said predetermined distance is approximately one-halfinch.
 37. The process claimed in claim 35, further comprising forming asecond flute diametrically opposite said first flute in said bit stockusing the same process set forth in claim
 35. 38. The process claimed inclaim 34, wherein said predetermined angle lies in the range of fromabout 20° to about 40°.
 39. The process claimed in claim 38, whereinsaid predetermined angle is about 30°.
 40. The process claimed in claim34, including grinding the flute such that the web thickness has auniform taper rate lying in the range of from about 0.050 inch to about0.071 inch per inch of flute length over substantially the entire lengthof said flute.
 41. The process claimed in claim 34, including grindingthe flute such that the flute length is selected so that when drilling apiece of wood 1½ inch thick, the operator does not have to clear theflutes of saw dust and can drill through the entire thickness of thewood in one pass.